The invention relates to an electrically height-adjustable head rest device in a seat back of a motor vehicle seat. The head rest device comprises a head rest, one or two bars carrying said head rest, one cross member, which is connected to at least one bar and has an internal thread, and one motor-spindle unit comprising a spindle, which engages the internal thread.
Such a head rest device is known for example from the document DE 10 2006 047 170 A1. When the head rest device is mounted inside a seat back, the at least one bar is fixed by a sliding piece that is provided in an upper edge of the seat back and forms an outlet opening for the bar. The head rest device is further connected to carrying parts of the seat back frame. Usually, the motor-spindle unit is connected to the seat back frame. As a result, its allocation is fixed.
Prior to mounting, the motor-spindle unit is not fixed though; it can rotate about the spindle and thus adopt any position with respect to the head rest. Irrespective thereof, some vehicle manufacturers would like that the motor-spindle unit needs not be connected to the structure of the seat back but that fastening rather occurs otherwise, in particular only through the sliding pieces mentioned. In this case, free rotation of the motor-spindle unit must be avoided. Other vehicle manufacturers want to be supplied with complete head rest devices that are to be delivered in a given condition, for example with the head rest in a completely retracted position. Only in this condition but not in the condition in which the head rest is completely extended, the motor-spindle unit must be allocated to the other parts for shipment and delivery, meaning it is not allowed to rotate freely. When the head rest is raised in the position in which it is spaced the greatest distance from the upper edge of the seat back, such a guide is not needed since the motor-spindle unit is fixed to the seat back in the mounted condition. Finally, some manufacturers want a guide between motor-spindle unit and cross member as a matter of principle, irrespective of their specifications regarding the delivery condition; others again do not want any guide.
Accordingly, the manufacturer of the head rest device must adapt to different wishes of the vehicle's manufacturer. In order to simplify the production of the very head rest device, it would be convenient to provide for a head rest device that would cover almost all the demands of the current automotive manufacturers. This is where the invention comes in.